im here again. THANK YOU SM (Crxxom) for helping me. you'll make me pass 7th grade!

Answer:
7.6cm
Step-by-step explanation:
Let's see - the midpoint of AB lies 10cm/2 from B and the midpoint of BC lies 5.2cm/2 from B in the other direction.
We can conclude that the midpoints are distant by
10cm/2 + 5.2cm/2 = 5cm + 2.6cm = 7.6cm